1,6' OAPT. 0. F. U. ]\!EEK ON THE 



chromosomes, again divisible into three groups as regards size. The fourth 

 largest o£ the complex is undoubtedly the heterotropic chromosome. The 

 distinct correspondence between the size and shape relationships of the 

 secondary spermatogonia! and primary spermatocyte complexes points to 

 the possibility of a lateral conjugation o£ members of the spermatogonia! 

 pairs during the intervening period, but is not a proof of it. 



9. The ordinary chromosomes divide in the primary spermatocyte meta- 

 phase, and their halves pass to opposite poles o£ the spindle : the heterotropic 

 chromosome shows no sign of division, and passes entire to one daughter cell, 

 while the ordinary chromosomes are still on the equatorial plate. In tbis 

 manner dimorphism of the subsequent spermatozoa is effected. 



10. I have been unable to discover whether reduction — the separation of 

 conjugant members — occurs at the first maturation division or at the next ; 

 possibly both divisions are equational, and only a numerical reduction 

 takes place as a result of lateral association of chromatin granules or 

 masses on the reticulum threads prior to the primary spermatocyte propha,se 

 of mitosis. 



11. There is no resting-stage between the first and second maturation 

 divisions ; the constriction of the cytoplasm to form the two daughter 

 secondary spermatocytes is closely followed by the appearance of the next 

 karyokinetic spindle. 



12. The complex of the secondary spermatocyte cell shows nine or eight 

 chromosomes, and this difference is due to the presence or absence of 

 the heterotropic chromosome, which is found in only 50 ^Jq of the cells. 

 The chromosomes exhibit the same size relationships that occurred in the 

 previous metaphases, there being three large chromosomes, three small, and 

 two of intermediate size, Tiie heterotropic chromosome, when present, is 

 the fourth largest of the complex. Two of the three small chromosomes are> 

 spherical, and the third is ovoid or slightly dumb-bell shaped : the remainder 

 appear as two arms jointed at one end and closely apposed to one another. 



13. I find no direct evidence to prove that these arms are the represen- 

 tatives of the spermatogonial pairs. 



14. Division occurs at the junction of the component arms. The hetero- 

 tropic chromosome usually "lags," and can be seen on the spindle when the 

 ordinary chromosomes have passed to the two opposite poles. 



15. The formation of the nuclear membrane in the spermatids is followed 

 by resolution of the ordinary chromosomes into their component granules. 

 This process continues until the nucleus appears of an uniformly grey colour, 

 in which the individuality of the chromatin particles is lost. The hetero- 

 tropic chromosome remains at first as a darkly staining and irregular body, 

 but later undergoes resolution into particles, whose identity is indistinguish- 

 able in the common chromatin mass. 



16. The appearance of the " centrosome '^ is followed by the formation of 



